The present invention relates generally to wireless communications, and more particularly, to precoding for physical layer multicasting.
Next generation wireless networks will require a spectrally efficient physical layer multicasting scheme in order to cater to important emerging applications such as real-time video broadcast, wherein a common information needs to be simultaneously transmitted to multiple users. The design of spectrally efficient physical layer multicasting schemes via instantaneous rate maximization has consequently received significant recent attention.
Referring to the diagram of FIG. 1A, there is shown an exemplary multicast communication over a cellular downlink. Notice that a single source communicates with multiple receivers on the same channel. In particular, in multicasting the source is interested in conveying the same message to all the users. This can be done by sending (or transmitting) the message to one user at a time but this approach leads to significantly degraded throughput (or spectral efficiency). On the other hand, simultaneously sending the message to all users is spectrally efficient but there are some key challenges that need to be overcome before these spectral efficiency gains can realized: optimizing the signal attributes such that the transmitted signal is suitable for all users, conveying the attributes of the transmitted signal to the users when only limited signaling related information can be conveyed; complexity constraints at the transmitter and at the users which necessitate that the optimization of signal attributes can be done with a low complexity by the transmitter, and that each user can receive the transmitted signal reliably with a decoding complexity not exceeding its respective complexity constraint.
Others have proposed: 1) Sequential transmission of the common message wherein the common message is transmitted to one user at a time after optimizing the signal attributes considering only that intended user; 2) Simultaneous transmission of the common message after assuming each user has only one receive antenna, which in turn imposes a rank one constraint on the signal attributes; 3) Simultaneous transmission of the common message using a simple heuristic which can lead to sub-optimal performance.
Accordingly, there is a need for improved precoding for multicast communication over a cellular downlink.